The present invention is generally directed to toner compositions and processes thereof, and more specifically, to colored encapsulated toner compositions and processes thereof, and wherein toners can be directly generated without resorting to the conventional pulverization and classification methods. In one embodiment, the present invention relates to colored encapsulated toner compositions which display low gloss levels of, for example, from about 1 gloss unit to about 15 gloss units, and more preferably from about 3 gloss units to about 14 gloss units, as measured by the Gardner.TM. gloss unit apparatus. In another embodiment, the present invention relates to a process of preparing colored encapsulated toner of fine particle size of from about 0.5 micron to about 15 microns in diameter, and more preferably from about 2 microns to about 7 microns diameter, as measured by a Counter Counter. In another embodiment, the present invention relates to colored encapsulated toner compositions which display low fixing temperatures of from about 110.degree. C. to about 150.degree. C., thereby reducing the energy consumption of an electrostatographic imaging or printing apparatus and prolonging the lifetime of the fuser contained therein. Furthermore, in another embodiment, the present invention relates to a colored encapsulated toner composition and process of generating an inner shell material surrounding a core material and wherein the resulting composite is surrounded by an outer shell or coating material. The colored encapsulated toners of this invention in embodiments are comprised of a core comprised of a polymer resin and colorants, including color pigments, dyes, or mixtures thereof, an inner shell material comprised of, for example, a polyurea, a polyurethane or a polyester and the like, and an outer coating layer comprised of a cellulose component, such as methyl cellulose, hydroxypropyl cellulose, hydroxyethylmethyl cellulose, and the like. The processes of the present invention in embodiments thereof are comprised of an initial dispersion step for forming a stabilized organic microdroplet suspension comprised of pigment, dyes or colorant, free-radical monomers, and an inner shell forming monomer such as a diisocyanate suspended in an aqueous medium containing an outer coating material, such as hydroxyethylmethyl cellulose; followed by addition of the second monomer forming the inner shell material by interfacial polymerization step, such as a diamine; and a final core resin formation step by free radical polymerization. The precipitation of the outer coating cellulose molecules is believed to begin at the initial dispersion-stabilization stage, and continues during the inner shell formation and core resin forming free radical polymerization step. In embodiments, the processes of the present invention can also utilize a mixture of cellulose polymers of from about 0.1 percent to about 5 percent by weight of the toner, and ionic or inorganic surfactants of from about 0.01 percent to about 0.5 percent by weight of toner, such as potassium oleate, sodium dodecyl sulfate, and the like during the dispersion step. The cellulose-ionic or inorganic surfactant system facilitates efficient generation of very small sized microdroplets, particularly those with an average particle diameter of from about 0.5 micron to about 7 microns, together with a narrow particle size distribution of less than 1.35 , as measured by the Counter Counter.
The primary function of the inner shell of the colored encapsulated toner of the present invention is to provide for the mechanical integrity of the toner, minimizing or eliminating the seepage of the inner core material, hence preventing toner aggregation or coalescing, as well as providing the low gloss properties to the toner image, highly desired in black and highlight reprographic technologies utilizing a VITON.RTM. roll fuser. The primary function of the outer cellulose shell for the colored encapsulated toner compositions prepared by the processes of the present invention is to provide additional low gloss or preferably a matte finish. In addition, this outer coating shell is selected to provide additional mechanical integrity to the toner compositions, and ensure effective protection with the inner shell material for the containment of the core components. In addition, the coatings also inhibit toner particles from coalescing and prevent, or minimize toner agglomeration during the dispersion step and interfacial polymerization step for generating the inner shell. The primary function of the outer shell coatings relates to the nullification, or passivation of the triboelectric charging effects of colorants present in the toner compositions, such that the triboelectric charging characteristics of the toner compositions are primarily controlled or dominated by the charging effects of the cellulose layer, and surface additives. Accordingly, the processes of the present invention are useful for the preparation of a wide variety of colored toners possessing similar or substantially similar triboelectric charging characteristics with a selected carrier, irrespective of the nature of the colorants present in the toners. For single component development where triboelectric charging is generally accomplished by a frictional charging blade, similar equilibrium triboelectric charge levels can also be obtained under substantially identical conditions with different colored toners of the present invention. The cellulose coating for the toner compositions obtained by the processes of the present invention are in general relatively thin in nature, its presence therefore does not substantially affect the toner's fusing characteristics.
In color reprography, such as in full color or highlight color applications, colored toners with a wide variety of colors including black are usually employed. In color reprography, a heat-assisted transfix step or heat-roll fusing is applied to the toner image on paper. It is highly desirable to use VITON.RTM. fuser rollers rather than the conventional silicone roll fusers due to the drastically prolonged lifetime attained by a fuser roll containing VITON.RTM. surfaces. During the fixing step employing heated VITON.RTM. roll fusers, the toner is fixed on paper and the energy necessary to achieve this is related to the temperature applied by the rolls. Accordingly, toners which fix on paper with minimum amount of heat are highly desirable. The temperature necessary to properly fix a particular toner onto paper is known as the minimum fixing temperature (MFT). It is known that encapsulated toner compositions are highly desirable for low minimum fixing applications, such as from about 110.degree. C. to about 150.degree. C., and preferably from about 110.degree. C. to about 130.degree. C. The aforementioned encapsulated colored toners are comprised of an inner core with low glass transition temperature resin for fixing the toner onto paper at the low aforementioned minimum fixing temperatures, in that the core of the encapsulated toner is surrounded by a shell material thereby avoiding agglomeration of the core materials during, for example, storage or until its use in the final fixing step. Toner fusing onto paper is accomplished by the melting of the toner and its penetration into the paper fiber, and sticking or adherence of the resin onto the paper with colorants, dyes and additives. After this fixing step, the surface of the toner image on paper is usually smooth, and in addition, paper calendering results especially when excessive pressure is applied by the fuser, such that the toner image surface and paper is very smooth. This aforementioned fixing mechanism is responsible for high gloss properties to the toner image, such as from about 40 gloss units to about 80 gloss units, as measured by the GARDNER.TM. gloss unit. The gloss level is proportional to the smoothness of the toner image after fixing, and can easily be measured using a known GARDNER.TM. gloss unit. In color reprography, such as full or pictorial color applications, high gloss is highly desirable such as from about 40 gloss units to about 80 gloss units and more preferably from about 45 to about 60 gloss units, as measured by the GARDNER.TM. gloss unit on toner image after fixing. When using colored conventional toners for full or pictorial colored applications, high gloss is easily achieved, and the use of colored encapsulated toners comprised of a core containing resin, pigment, dyes or colorant and optionally surrounded by a shell for full color or pictorial applications, high gloss can be achieved. For color reprography, wherein black or highlight color application is desired, low gloss is desired, and preferably low gloss of less than 14 gloss units and more preferably less than 11 gloss units as measured by the GARDNER.TM. gloss unit. Gloss values of from about 14 gloss units and below are usually known to those in the art as "matte finish". However, both the aforementioned conventional and prior art encapsulated colored toners do not exhibit low gloss values, and are inferior to black and highlight color reprographic technologies which utilizes VITON.RTM. roll fusers. The colored encapsulated toner compositions of this invention alleviate the problem of high gloss and provide low gloss black and highlight colored images, and more preferably of a matte finish when transfixed using VITON.RTM. fuser rolls. Furthermore, the colored encapsulated toners of this invention can be of a fine average particle size of from about 0.5 micron to about 9 microns and more preferably from about 2 microns to about 7 microns in diameter, unattainable economically by conventional pulverization process. Additionally, the encapsulated toner compositions of this invention display low minimum fixing characteristics with excellent tribo characteristics such that the triboelectric properties of different colored toners be desirably controlled so that they all attain similar equilibrium triboelectric charging levels when utilized with a selected carrier. This is especially useful for custom colored toner packages since colored toners with a wide variety of custom colors can be obtained by simple blending of the primary colored toners. Another important aspect for two component development is the rate of charging of new toner to equilibrium charge levels when they are added to the toner depleted development housing. A fast rate of charging of fresh toner can be important in ensuring proper image development, particularly for high speed, greater than 70 copies per minute for example, reprographic systems.
It is known that color pigments or dyes present in the toner have a dominant effect on the toner's triboelectric charging behavior, arising primarily because these colorants are often also present at or close to the surface of the toner, and are, therefore, exposed to their environments. As a consequence, when the toner particles are admixed with carriers, the interactions of the exposed pigments of the toners with the carrier particles drastically affect the charging behavior of the toner. Similar effects are obtained for a number of prior art encapsulated toners where the color pigment particles are not completely encapsulated within the toner shell. Thus, it is often observed that toners with identical components, except colorants, exhibit different charging behavior, even to the extent of having triboelectric charges of opposite polarity. To overcome this difficulty, it is usually necessary to utilize different charge control additives for different colorants, or to use high levels of charge control additives so as to nullify or overcome the different charging effects of different colorants, and exert a dominating influence on the charging characteristics of the toners. The toners and processes of the present invention eliminate or overcome this difficulty through complete or substantially complete encapsulation of core components with an inner shell, and in addition, by the precipitation of an outer coating on the inner shell. As a consequence, the need to rely on only one shell material is avoided by the use of an additional outer layer precipitated coating of this invention. It is believed that the inner shell and outer shell precipitated coating, especially when TYLOSE.RTM. is employed, avoids toner smoothness after the fixing step, and alleviates unwanted gloss properties for black and highlight color reprographic technologies employing VITON.RTM. roll fusers. Other advantages associated with the toner compositions obtained by the processes of the present invention include, for example, rapid triboelectric charging rates, small toner size and narrow size distribution for high resolution images, excellent color mixing properties and image color fidelity, low minimum fusing temperatures, acceptable powder flow, and nonblocking and nonagglomerating characteristics. The toner compositions of the present invention can be selected for a variety of known imaging processes including electrophotographic and ionographic processes. It is also known that colored, including black single component magnetic toners, as well as encapsulated single component magnetic toners for ionographic applications, exhibit undesired high gloss properties, such as from about 40 gloss unit to about 80 gloss. This is primarily due to the high pressures exerted by the dielectric receivers on the toner image. The colored, including black, toners of this invention contain an additional outer coating not present in prior art toners, enabling the toner images with low gloss and preferably matte in finish.
Encapsulated toners and processes containing two shells are known. For example, U.S. Pat. No. 4,565,764 discloses a colored microcapsule toner composition and process thereof comprised of a core comprised of a wax and colorant, a first shell resin wall having an affinity for both the core and a second shell wall; and note column 3, line 13, wherein the first wall is chemically bonded to at least the second wall and core material, and note column 7, line 65, to column 8, line 5, wherein the first resin wall is oppositely charged to those of the core material and second resin wall. Furthermore, the microcapsules are prepared by a coacervation or phase separation process. U.S. Pat. No. 4,797,339 discloses a toner comprising an inner layer comprising a resin ion complex having a colorant and ionically crosslinked with a resin of opposite charge, and containing an outer layer comprised of flowability imparting agent. Similarly, U.S. Pat. No. 4,996,127 teaches a process of producing microcapsule toner composed of associated particles of secondary particles comprising primary particles of a polymer having an acidic or basic polar group, coloring agent and charge controlling agent. With the present invention in embodiments, the inner shell and outer shell are not chemically or ionically bound, and contain an interfacial polymer resin, such as a polyurea, for low gloss attributes, and also the outer coating material, such as TYLOSE.RTM., is not believed to be disclosed in '497, '764 or '127, which TYLOSE.RTM. is selected for low gloss and triboelectricity control. Additionally, the microcapsule of this invention is prepared by a suspension free-radical process, followed by interfacial polymerization, and coating thereof. Encapsulated toners and processes containing one shell are also known, for example, both U.S. Pat. No. 4,626,489 and British Patent 1,538,787, as well as U.S. Pat. No. 4,766,051 disclose similar processes for colored encapsulated toners wherein both the core resin and shell material are prepared by suspension polymerization techniques. However, only one shell material is present in the toner compositions of the aforementioned prior art. Similarly, other prior art, such as U.S. Pat. No. 4,727,011, discloses a process for preparing encapsulated toners which involves a shell forming interfacial polycondensation and a core binder forming free radical polymerization; and U.S. Pat. No. 4,708,924 discloses the use of a mixture of two polymers, one having a glass transition temperature in the range of -90.degree. C. to 5.degree. C., and the other having a softening temperature in the range of 25.degree. C. to 180.degree. C., as the core binders for a pressure fixable encapsulated toner. Other representative U.S. Pat. Nos. are: 4,339,518, which relates to a process of electrostatic printing with fluorinated polymer toner additives where suitable materials for the dielectric toner are thermoplastic silicone resins and fluorine containing resins having low surface energy; U.S. Pat. No. 4,016,099, which discloses methods of forming encapsulated toner particles and wherein there are selected organic polymers including homopolymers and copolymers, such as vinylidene fluoride, tetrafluoroethylene, chlorotrifluoroethylene, and the like; U.S. Pat. No. 4,497,885, which discloses a pressure fixable microcapsule toner comprising a pressure fixable component, a magnetic material, and other optional components, and wherein the core material can contain a soft material, typical examples of which include polyvinylidene fluoride, polybutadiene, and the like; U.S. Pat. No. 4,520,091, which discloses an encapsulated toner with a core which comprises a colorant, a dissolving solvent, a nondissolving liquid and a polymer, and may include additives such as a fluorine containing resin; and U.S. Pat. No. 4,590,142 relating to capsule toners wherein additives such as polytetrafluoroethylenes are selected as lubricating components. Furthermore, there are disclosed in the prior art encapsulated toner compositions containing costly pigments and dyes, reference for example the color photocapsule toners of U.S. Pat. Nos. 4,399,209; 4,482,624; 4,483,912 and 4,397,483.
In a U.S. Pat. No. 5,175,071 (D/90516), the disclosure of which is totally incorporated herein by reference, a colored encapsulated toner comprised of a core resin and colorant, coated with a cellulose shell material is disclosed, and wherein no inner shell material is present and low gloss properties are not disclosed. Furthermore, the gloss properties with the colored encapsulated toner compositions of this patent, containing only one shell are not attained generally as illustrated herein.
The following U.S. patents located in a patentability search report for encapsulated toners are mentioned: U.S. Pat. No. 4,967,962, which discloses a toner composition comprising a finely divided mixture comprising a colorant and a polymeric material which is a block or graft copolymer, including apparently copolymers of polyurethane and a polyether (column 6), reference for example the Abstract of the Disclosure, and also note the disclosure in columns 2, 3, 6 and 7, particularly lines 13 and 35; however, it does not appear that encapsulated toners are disclosed in this patent; 4,626,490 contains a similar teaching as the '764 patent, and more specifically, discloses an encapsulated toner comprising a binder of a mixture of a long chain organic compound and an ester of a higher alcohol and a higher carboxylic acid encapsulated within a thin shell, reference the Abstract of the Disclosure, for example, and note specifically examples of shell materials in column 8, beginning at line 64, and continuing on to column 9, line 17, which shells can be comprised, for example, of polyurethanes, polyurea, epoxy resin, polyether resins such as polyphenylene oxide or thioether resin, or mixtures thereof; U.S. Pat. Nos. 4,442,194 and 4,465,755, mentioned herein; and U.S. Pat. Nos. of background interest including 4,520,091; 4,590,142; 4,610,945; 4,642,281; 4,740,443 and 4,803,144.
Furthermore, other prior art, primarily of background interest, includes U.S. Pat. Nos. 4,254,201; 4,465,755 and Japanese Patent Publication 58-100857. The Japanese publication discloses a capsule toner with high mechanical strength, which is comprised of a core material including a display recording material, a binder, and a shell, which shell is preferably comprised of a polyurea resin. In the U.S. Pat. No. '201 there are disclosed encapsulated electrostatographic toners wherein the shell material comprises at least one resin selected from polyurethane resins, a polyurea resin, or a polyamide resin. In addition, the U.S. Pat. No. '755 discloses a pressure fixable toner comprising encapsulated particles containing a curing agent, and wherein the shell is comprised of a polyurethane, a polyurea, or a polythiourethane. Moreover, in the U.S. Pat. No. '201 there are illustrated pressure sensitive adhesive toners comprised of clustered encapsulated porous particles, which toners are prepared by spray drying an aqueous dispersion of the granules containing an encapsulated material.
Also, in U.S. Pat. No. 4,599,271, the disclosure of which is totally incorporated herein by reference, there are illustrated microcapsules obtained by mixing organic materials in water emulsions at reaction parameters that permit the emulsified organic droplets of each emulsion to collide with one another, reference the disclosure in column 4, lines 5 to 35. Examples of polymeric shells are illustrated, for example, in column 5, beginning at line 40, and include isocyanate compounds such as toluene diisocyanate, and polymethylene polyphenyl isocyanates. Further, in column 6, at line 54, it is indicated that the microcapsules disclosed are not limited to use on carbonless copying systems; rather, the film material could comprise other components including xerographic toners, see column 6, line 54.
Illustrated in U.S. Pat. No. 4,758,506, the disclosure of which is totally incorporated herein by reference, are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process. In U.S. Pat. No. 5,043,240, the disclosure of which is totally incorporated herein by reference, there are illustrated encapsulated toners with a core comprised of a polymer binder, pigment or dye, and thereover a polymeric shell, which contains a soft and flexible component, permitting, for example, proper packing of shell materials resulting in the formation of a high density shell structure, which can effectively contain the core binder and prevent its loss through diffusion and leaching process. The soft and flexible component in one embodiment is comprised of a polyether function. Specifically, in one embodiment there are disclosed in the aforementioned patent encapsulated toners comprised of a core containing a polymer binder, pigment or dye particles, and thereover a shell preferably obtained by interfacial polymerization, which shell has incorporated therein a polyether structural moiety. Another specific embodiment of the patent is directed to encapsulated toners comprised of a core of polymer binder, pigment, dye or mixtures thereof, and a polymeric shell of a polyether-incorporated polymer, such as a poly(ether urea), a poly(ether amide), a poly(ether ester), a poly(ether urethane), mixtures thereof, and the like.
Many of the prior art encapsulated toner compositions, in particular colored toner compositions, suffer from a number of deficiencies as indicated herein. For example, these toners do not possess, it is believed, desirable low gloss of from about 14 gloss units and below and more preferably less than 11 gloss units or a matte finish in color reprography utilizing VITON.RTM. fusers. The prior art encapsulated toner compositions contain only one shell material, or do not contain an inner shell material and outer shell material to enable low gloss applications, such as from about 1 gloss unit to about 14 gloss units. The gloss property of some of the prior art colored encapsulated toner compositions containing only one shell are reported in the Comparative Examples, and wherein the desired low gloss properties of from about 1 gloss unit to about 14 gloss units are not attained. Also, many of the prior art encapsulated toners do not display fusing properties such as being able to be fused at a reasonably low temperature of, for example, less than 160.degree. C.; they usually require different or excessive amounts of charge control agents for different colored toners; and their rates of triboelectric charging are poor. In addition, some prior art colored encapsulated toners cannot be obtained in smaller toner size of, for example, less than 7 or 8 microns in diameter with a narrow size distribution of less than about 1.35, and more preferably of from about 2 to about 7 microns with a narrow size distribution of less than about 1.35 in a cost effective manner. Also, toner blocking or agglomeration may be a problem with several of the prior art encapsulated toners because of the porosity of the shell structure, especially when they are exposed to conditions of elevated temperatures. Further, some of the prior art colored encapsulated toners are comprised of colored pigment particles that may not completely be encapsulated by the shell, and the triboelectric charging effects of such pigments are, therefore, not fully passivated, and this would adversely affect and degrade the toner triboelectric characteristics, thereby causing image quality to deteriorate. In addition, many of the prior art toner compositions do not possess the necessary long-term physical and environmental stability. These and other disadvantages are eliminated or substantially eliminated with the process and toner compositions of the present invention.
There is a need for colored toners which display low gloss values and are preferably matte finish, especially with color reprographic systems employing VITON.RTM. fuser rolls. Additionally, there is a need for color toners with low minimum fusing temperatures, wide fusing latitude, of fine particle size, of nonblocking tendencies, and of stable triboelectricity properties including complete passivation. These and other needs are accomplished with the colored encapsulated toners and process thereof of the present invention. More specifically, thus with the toners of the present invention, the toner properties can in many instances be tailored to certain specifications. Specifically, with the toners of the present invention in embodiments, low gloss images of matte finish are attainable with reprographic technologies employing VITON.RTM. fuser rolls. Additionally, complete or substantial passivation of the triboelectric charging effects of the colorants is accomplished, and smaller toner particle size with narrow size distribution can be achieved without conventional classification techniques. Also, the toners of the present invention do not block or agglomerate over an extended period of time, for example up to six months, in embodiments.